The Drosophila gypsy retrovirus will be used as a model system for the study of the processes underlying retrovirus regulatory evolution. Regional duplications within the cis-regulatory regions located in the long terminal repeat (LTR) and/or translated leader region (ULR) is a characteristic feature of retrovirus regulatory evolution. Gypsy elements within Drosphila melanogaster popluations are in the process of evolving new regulatory sequences which provides a unique opportunity to study retroviral regulatory evolution in progress. Such cis-regulatory changes seem to be an adaptive response to host (chromatin dependent) silencing mechanisms. We proposed to utilize the gypsy model to investigate the molecular and population genetic principles underlying retrovirus regulatory evolution.